The invention relates to an apparatus for PID address protection, and more particularly, to an apparatus and a method for protecting a plurality of physical identification data synchronous signals by counting a plurality of data synchronous signals or number of frames in an optical storage system.
As information and multimedia technology progresses, so too does the storage needs—i.e. storage densities and capacitances of storage devices—of computers, communication equipment, and consumer products. A storage device with high storage density, small size, and low cost is more and more necessary for today's information flows. As a result, an optical storage medium such as an optical disc has been one of the most common storage mediums in recent years because of its small volume and weight, and low cost. Especially with the invention of CD-R, which allows users to write data on an optical disc according to their needs, the optical disc has become one of the most important portable and personal storage mediums. As a result, how to make the data accessing of the optical disc more reliable and efficient is the research focus in the industry now.
Digital versatile discs (DVD), which, with its high capacity and definition, is widely used for backup and playing and storing video data, is currently the best optical storage medium. The standards of digital versatile discs (DVD) include DVD-R, DVD-RAM, DVD-RW, and etc, which all have many characteristics in common. Similar to the CD, a DVD has a plurality of tracks for storing data. Additionally, in order to manage stored data easily, sectors in each track are utilized to accomplish stored-data planning. Each sector can be divided into many frames, and the information is stored in each frame of the DVD.
For example, in an optical disc of DVD-RAM, each sector is about 2700 bytes, and a header composed of complementary allocated pit addresses CAPA is in the front of each sector. Please refer to FIG. 1, which is a diagram of each sector 10 in a DVD-RAM optical disc according to the prior art. Each sector 10 of a DVD-RAM optical disc includes two main parts: a header 12 and a data-storing area 14 used for storing data. The information in the header 12 includes the physical position of the sector 10 of a DVD-RAM optical disc because if an optical storage system reads data from the DVD-RAM optical disc or writes data into the DVD-RAM optical disc, the optical storage system first has to know the correct position corresponding to the data in order to complete the read/write operation.
In a determined standard of DVD-RAM, the header 12 occupies 128 bytes, and the data-storing area 14, which has the biggest storing space, occupies 2418 bytes. In addition to the header 12 and data-storing area 14, the sector 10 further includes a PS synchronous signal area (PS). A PS, being 3 bytes and located before the data-storing area 14, is used to provide a synchronization timing for detecting the data-storing area 14 next to the PS.
Please refer to FIG. 2, which is a detailed diagram of the header 12 in FIG. 1. The header 12 is divided into four sub-headers, respectively the first sub-header H1, the second sub-header H2, the third sub-header H3, and the fourth sub-header H4. Each sub-header H1˜H4 includes a voltage frequency oscillator (VFO) area, an address mark (AM) area, a physical identification data (PID) area, an identification error detection (IED) area, and a PA area. For example, the first sub-header H1 includes a first voltage frequency oscillator (VFO1) area, a first address mark (AM1) area, a first physical identification data (PID1) area, a first identification error detection (IED1) area, and a first PA (PA1) area. The second, third, and fourth sub-headers are similar to the first sub-header. In a sub-header, each physical identification data (PID) area stores a PID, which includes the most important address information that can be used for being an address reference of an optical pick up head when accessing data. Additionally, the address mark (AM) area is positioned in front of the PID area for providing a physical identification data synchronous signal PIDS, (also called an address mark signal AM signal) to be a synchronous timing for detecting the physical identification data (PID). Therefore, for accurately decoding the PID stored in each sub-header H1˜H4, the AM area of each sub-header H1˜H4 has to be detected first, and then the PIDS generated by the AM area is utilized for decoding the following PID to read/write data.
A DVD-RAM standard is taken as an example again. Information stored in DVD-RAM is an eight-to fourteen modulation plus (EFM+) data signal. Generally speaking, in prior art, the eight-to fourteen modulation plus (EFM+) data signal is a signal type generated by an optical pickup module (not shown in the FIG. 1) in an optical storage system (such as a DVD drive) after reading related information on the data tracks of DVD-RAM. In the DVD standard, the EFM+ data signal can be regarded as having the data type shown in FIG. 1. The header 12 of each sector 10 (especially the first sub-header H1) represents the initial position of the sector 10.
Please refer to FIG. 1 again, FIG. 1 also shows four impulse signals corresponding to the header 12 in FIG. 1. The four impulse signals are respectively a first physical identification synchronous signal PIDS1, a second physical identification synchronous signal PIDS2, a third physical identification synchronous signal PIDS3, and a fourth physical identification synchronous signal PIDS4. And the four physical identification synchronous signals PIDS1˜PIDS4 are respectively generated by detecting the first address mark area to the fourth address mark area AM1˜AM4. In the normal procedure of demodulating the EFM+data signal, four physical identification data synchronous signals PIDS1˜PIDS4 have to be detected. This means that PIDS1˜PIDS4 (such as the four impulses PIDS1˜PIDS4 shown in FIG. 1) are generated in sequence for detecting the following: first to the fourth PID. However, because of defects of DVD-RAM or noises of the system, the related optical pickup module incorrectly detects things (such as the impulse MS shown in FIG. 1) as physical identification data synchronous signals PIDS in the non-headers(or in the incorrect position of headers 12) so that incorrect data are regarded as a PID and an error in the addressing operation of the optical pickup head occurs.